Internal interconnecting shafts are major parts of gas turbine engines. Their prime purpose is to transmit driving power from the turbine to the compressor end of a rotor. Within a two or three shaft engine the innermost rotor is the low pressure (LP) rotor which transmits power from the LP turbine to the fan or LP compressor. Typically, the LP shaft carries the highest torque load of any of the shafts.
Shaft joints may have to carry a combination of torque, axial load and bending moment. Three basic types of joint are in use, namely: bolted joints, splines and curvic couplings. Bolted joints are relatively low cost, but splined and curvic couplings have higher torque-carrying capabilities due to their use of interlocking teeth.
FIG. 1 shows schematically a longitudinal cross-section through the rear portion of a low pressure shaft of an engine. A cylindrical section 100 of the rear portion extends forwardly towards the compressor end of the rotor. At the rear end of the cylindrical portion, the shaft has an aft section 102 or “cone” whose diameter expands progressively with distance along the rearward direction of the engine to terminate in one side of an annular curvic coupling 104. The other side of the coupling is the inner end of a drive arm 106 which extends, coaxially with the shaft, radially inwardly from the low pressure turbine 108 of the engine. A stubshaft 110 extending rearwardly from the joint provides a location for supporting bearings (not shown) for the shaft.